1. Field of the Invention
This invention relates to silarylene-siloxane prepolymers, silarylene-siloxane-acetylene precursors, silarylene-siloxane-acetylene networked polymers, silicon-containing ceramic compositions, and processes for making the same.
2. Description of the Related Art
Functionalized organosilicon polymers represent a diverse class of materials that have found widespread use in a variety of applications, ranging from contact lenses, to medical implant devices to high-temperature materials for automotive and aircraft parts. Polysiloxanes or silicone polymers have been mostly studied and are of the greatest commercial importance. A major limitation of organosiloxane polymers is their limited long-term thermal stability at temperatures in excess of 200xc2x0 C. caused primarily by ionic degradation reactions and formation of stable cyclic products such as six- and/or eight-membered siloxane rings. To improve long term thermal stability at high temperatures while retaining low temperature flexibility, various investigations have been directed toward the incorporation of aromatic units into the backbone or into the pendant groups to prevent formation of the cyclic products. However, some synthesis routes for these aromatic organosilicon polymers still result in degradative side reactions that limit molecular weight.
Silarylene-siloxane polymers, xe2x80x94[Si(R2)xe2x80x94Arxe2x80x94{Si(R2)xe2x80x94Oxe2x80x94}z]xe2x80x94, in which a fraction of the total content of siloxy oxygens in the polysiloxane chain are replaced by aromatic units, are the most studied class of aromatic containing polymers. Four primary routes for the syntheses of silarylene-siloxane polymers in which one of the aforementioned difunctional monomers is allowed to react with an arylene-disilanol have been disclosed: chlorosilane (Lai et al., J. Polym. Sci. Polym. Chem. Ed., 1982, 20, 2277), acetoxysilane (Rosenberg et al., Polym. Preprints, 1978, 19(2), 625), aminosilane (Burks et al., J. Polym. Sci. Polym. Chem. Ed., 1973, 11, 319), and ureidosilane (Dvornic et al., W. J. Polym. Sci. Polym. Chem. Ed., 1982, 20, 951) polycondensation methods. The occurrence of degradative side reactions between acidic by-products and the growing polymer chain has been shown to limit molecular weights and disrupt the truly alternating nature of the polymer structures prepared via the former two methods. The aminosilane method produces a weakly basic by-product. The ureidosilane route has been reported to be the method of choice for producing high-molecular weight linear silarylene-siloxane polymers with exactly alternating structures. The success of the ureidosilane method is due to the formation of an unreactive polycondensation by-product that reduces the occurrence of degradative side reactions.
Zhang et al. disclosed a process of making high-molecular-weight silphenylene-siloxane homopolymers and copolymers via dehydrocoupling polymerization using Wilkinson""s catalyst ((Ph3P3)RhCl). (Macromolecules 2000, 33, 3508). The compositions were made using a 1:1 molar ratio of the two monomers and did not have specific terminating groups. U.S. Pat. No. 5,874,514 to Keller et al. discloses linear inorganic-organic hybrid polymers having repeat units that contain at least one alkynyl group and at least one siloxanyl group within the backbone. U.S. Pat. No. 5,563,181 to Keller et al. discloses inorganic-organic hybrid thermoset polymers that are formed from linear inorganic-organic hybrid polymers having repeat units that contain at least one alkynyl group for cross-linking purposes and at least one siloxanyl group. U.S. Pat. Nos. 5,346,980 and 5,578,380 to Babu disclose crosslinkable copolymers suitable for use as elevated temperature pressure-sensitive adhesives comprising randomly arranged silarylene units and siloxane units. U.S. SIR H1612 to Rhein et al. discloses a method of making silarylene-siloxane polymers.
There is a need for oxidatively stable crosslinked silarylene-siloxane networked polymers. The networked polymers should be made by a process that avoids degradative side reactions that limit molecular weight and reduce performance at high temperatures. Such networked polymers are useful for high temperature plastics, elastomers, adhesives, and coatings. There is also a need for a hydroxy-terminated prepolymer needed to form the networked polymers. There is a further need for a ceramic composition formed from such networked polymers. Such materials would be useful in reinforced composites.
An object of the invention is to provide oxidatively stable silarylene-siloxane-acetylene networked polymers suitable for use as high temperature plastics, elastomers, adhesives, and coatings, capable of retaining their elastomeric properties up to 250xc2x0 C.
A further object of the invention is to provide prepolymers and precursors that are needed to form the networked polymers of the invention.
A further object of the invention is to provide ceramic compositions, made by pyrolysis of the networked polymers, that are useful in reinforced composites.
A further object of the invention is to provide processes for making the networked polymers, prepolymers, and precursors of the invention, while avoiding degradative side reactions.
These and other objects of the invention are accomplished by a networked polymer comprising the formula: 
wherein nxe2x89xa71;
wherein n is an average value obtained by averaging all repeating units of the networked polymer;
wherein mxe2x89xa71;
wherein Y is a divalent group containing one or more acetylenic groups, one or more crosslinks, or both;
wherein z is the average number of crosslinks per Y group;
wherein Ar1 and Ar2 are independently selected aromatic groups; and
wherein each R is independently selected from the group consisting of alkyl, aryl, alkylaryl, haloalkyl, haloaryl, and combinations thereof.
A further embodiment of the invention is a precursor comprising the formula: 
wherein nxe2x89xa71;
wherein n is an average value obtained by averaging all repeating units of the precursor;
wherein mxe2x89xa71;
wherein X is a divalent group containing one or more acetylenic groups;
wherein Ar1 and Ar2 are independently selected aromatic groups; and
wherein each R is independently selected from the group consisting of alkyl, aryl, alkylaryl, haloalkyl, haloaryl, and combinations thereof.
A further embodiment of the invention is a prepolymer comprising the formula 
wherein nxe2x89xa71;
wherein T is either xe2x80x94H or xe2x80x94OH and both T""s are the same;
wherein Ar1 and Ar2 are independently selected aromatic groups; and
wherein each R is independently selected from the group consisting of alkyl, aryl, alkylaryl, haloalkyl, haloaryl, and combinations thereof.
A further embodiment of the invention is a ceramic composition formed by pyrolysis of the above networked polymer.
A further embodiment of the invention is a process for making the prepolymer, being a hydroxy-terminated prepolymer or a hydride-terminated prepolymer, comprising the step of reacting one or more arylenedisilanols with one or more bissilarylenes.
A further embodiment of the invention is a process for making the precursor comprising the step of reacting a hydroxy-terminated prepolymer with a bis(dimethylaminosilyl)alkyne.
A further embodiment of the invention is a process for making the networked polymer comprising the step of crosslinking the precursor.